1. Technical Field
Embodiments of the present invention relate to probe cards with probes used to test components on a wafer during manufacture. More particularly, the present invention relates to protection mechanisms for the probe card to prevent damage to the probes and to prevent damage to the wafer being tested.
2. Related Art
FIG. 1 shows typical components for testing a wafer using a probe card. The test system components include the probe card (or probe head) 2, the protective cover 4 attached to the probe card by screws 8, a probe card holder tray 10, wafer 12 and prober (or prober chuck) 14. The probe card 2 includes probes 6 for contacting pads of circuits on the wafer 12 to perform tests during fabrication of components before the wafer is diced up into the individual circuits (e.g., programmable logic devices) for packaging. The protective cover 4 is attached to prevent damage to the probes 6 during transportation of the probe card 2, and when the probe card 2 is not in use.
FIG. 2 shows the test typical components for testing the wafer 12 of FIG. 1, but with the protective cover 4 of the probe card 2 removed for testing. In FIG. 2, the probe card 2 is placed in the holder tray 10 so that the probes 6 and parts of the probe card 2 pass through an opening 11 in the holder tray. The probe card 2 is mounted in the holder tray 10 using attachment mechanisms not shown. During testing, the prober 14 operates to precisely lift the wafer 12 to contact the probes 6 of the probe card 2. The probes in one exemplary device extend 8 millimeters (0.315 inches) from the base of the probe card 2. The prober chuck 14 moves within precise limits to assure contact of circuits on the wafer 12, while preventing damage to the probes 6 or the circuits being tested.
FIG. 3 illustrates the effect if the probe card 2 is placed in the holder tray 10 and testing begins before the protective cover 4 is removed. The system shown allows the probe card 2 to be placed on the probe card holder tray 10 even when the probe head cover 4 is still on the probe card 2. The cover 4 and attachment screws 8 extend through the opening 11 in the probe card holder tray 10 significantly below the 8 millimeters depth of the probes 6. Accordingly, if testing is started before the cover 4 is removed, the wafer 12 can strike the attachment screws 8, possibly causing damage to both the wafer and to the probe card. An incorrect probe card depth (i.e., longer than the required depth of probes 6 in this case) can result in damage to the probe head and wafer 12 if the wafer 12 is lifted by the prober chuck 14. The thickness of the probe head cover 4 and two long screws 8 add to create a total depth to about 24 millimeters, or 0.900 inches, beyond the required 8 millimeter probe depth. Both the probe card 2, and wafer 12 with potentially hundreds of complex circuits are costly to replace.